Turtles -is a-> Long-Lived Species

There is a potential link between anoxia tolerance and longevity. The mechanisms used by turtles to survive anoxia can directly and indirectly be linked to their extraordniary longevity [20716943].

For instance, the processes used to protect the turtle brain against anoxia and subsequent reoxygenation might contribute to longevity. These selectively activated processes in turtles can be used as a model to investigate key mechanisms for protection against Aging [12855290]. By understanding the molecular mechanisms that play a role in hypoxia and anoxia tolerance in turtles, human health can be improved and their Lifespan extended [20716943].

:Abstract: Wonders of extraordinary long-lived species - will they ever end? Species adapted to their environments with a specific lifespan. Most species developed aging to speed up their evolution. Non-aging species normally would be out-competed by the aging species. However, in some biological niches longevity were acquired. It appears that numerous animal species evolved a remarkable feature of escaping the natural force of developing aging. The maximum lifespan of many of these long-lived species appear to be limited by our inability to record their life-history in capacity and the extrinsic force of mortality which is inverse to the intrinsic aging process. What can we learn from these long-lived species about human aging?

Introduction

Aging is presumably caused by accumulation of damage on various levels. All things are ageing. - All things? Not everything! Although aging is quite widespread, it is not an universal phenomenon. Nature is full of wonders. It generated a huge variety of species with very different lifespans. Some live just about a day, while others live thousands of years and some do not age at all! How is this possible? In order to understand this extraordinary circumstance, one first needs to ask very basic questions: Why we age and what is life actually? Then it is possible to realize that each species adapted to its environment with a specific lifespan. Most species developed aging to speed up their evolution. Non-aging species normally would be out-competed by the aging species. However, there are also many cases were longevity evolved or even immortality. Numerous animal species evolved the ability to escape the strong natural force of developing aging, because of their specific environment. New record-breaking lifespan limits are constantly reported and it seems that the maximum observed lifespan records are solely limited by the relatively short lifespan of our own species as well as the extrinsic forces of death such as predation and accidents. Also within the human species some individuals are genetically blessed with longevity. However, humans had failed to reach to ages above 122, while there exist animals that can live by far much longer and aging appears even to be negligible in some of them. What can we learn from these long-lived species about human aging? Unlocking their secret might reveal the most dominant causes of aging and help to develop effective strategies for making senescence also in our own species negligible.

Evolution works via replication, variation and selection (definition of live). A species replicates via reproduction and generates variants of itself by passive mutations as well as active recombination (sex shuffles the genomes). The replicates (offspring) are selected by the environment (in particular via predators and competitors) for those which are superior in their properties, whereas the others are eliminated. Natural selection forces on maintaining a functional body of a single individual after reproduction is thus not great as the genes are already passed to the next generation. However, there are a multitude of forces to actively limit lifespan. First of all, the parent generations are competing with their own offspring for the limited resources. Secondly, the parents are more experienced and would therefore have negative influence on the fitness of their progeny. Even a small fitness reduction due to aging would increase their probability to die (definition of aging) and then freeing up resources for the next generation. Therefore, aging was selected for. Aging evolved to speed up evolution. It allowed to maintain a higher generational turnover which means basically more rounds of replication, variation and selection (i.e. evolution) in a shorter time window [Weismann A: Ueber die Dauer des Lebens. Fisher, Jena, 1882].

Island of the Mortals and Immortals

If a non-aging species encounters an aging species and they both competing for shared resources (lets say on a isolated island), then the aging species would drive the non-aging species into extinction. This is why aging evolved and is so widespread.

The Evolution of Longevity

Examining species for their maximum recorded lifespan across the animal kingdom suggests in the first instance that body-size correlates with longevity, in that smaller-sized animals are short-lived, whereas bigger animals are long-lived [Figure 1]. Like a mouse lives 3 years, a dog 15 years, a horse 40 years and an elephant 70 years. It is a normal straight upward sloping line. However, there are exceptions of this simplified correlation. Many exception to be precise. Bats are like mouse in size but can live around 30 years. Some birds like parrots live 90 years. Humans just about the size of a large dog can live 122 years. Little turtle and deep dwelling rock fish can live 150 years and little lobster can live 220 years. Arctic claims can even live up to 250 years. What do they all have in common? They all have a great defence against predators, full body armour, extreme intelligence, flight and isolation.

Long-lived species arose due to the acquisition of special ecological niches. Thus, we now know the evolutionary why aging evolved and why longevity were in some cases selected for. However, what is the physiological why these long-lived species are so special? Many of the aging systems so common intact in aging species appear to be attenuated or eliminated in those organisms. We will discuss these aging systems with a few discrete example from birds, to naked mole rats, to turtles and finally some immortals.

Telomere Length in Birds Predicts Longevity
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Measuring telomere length periodically over the course of a zebra finch's life revealed a tight association between length and lifespan, particular at 25 days old. Measuring telomere length in zebra finches from nestling stage and at various points thereafter, revealed that telomere length at 25 days to be a very strong predictor of realized lifespan. Those individuals living longest had relatively long telomeres [Heidinger et al. 2012; http://www.ncbi.nlm.nih.gov/pubmed/22232671].

The Almost-Ageless Bird
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The marine bird Fulmar does not show any signs of aging or decline in reproductive function prior to death. It was separated on an island. Therefore, flight and isolation contributed to the attenuation of its aging systems. Strikingly this seabird displays non of the classical signs of aging. This species probably lost all its aging systems other then telomere-shortening.

The Arctic Pheonix
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A long-lived and very beautiful seabird, which lives at the harsh conditions of the arctic, shows little signs of senescence on sudden death, despite immense metabolic rate. These diving birds reach their 30s and then die quickly and suddenly, displaying few signs of aging. Guillemots look familiar to penguins but can fly, have the highest flight costs of any bird and expend substantial energy for diving. High metabolism and frequent dives should produce oxidative stress, causing deterioration of this bird as it ages. However, this birds stay fit and active as they grow older, maintaining their flying, diving and foraging abilities. Thus this birds life very long and maintain also their energetic lifestyle in a very extreme environment into old age [http://umanitoba.ca/news/blogs/blog/2012/07/03/diving-seabird-shows-good-way-to-live-then-suddenly-die/]. It is beautiful arctic Phoenix, which is really an appropriate designation for such an impressive creature.

Survival would be expected to decrease at higher latitutdes, but the longest-lived wild birds (albatrosses) [Ricklefs, 2008] and mammals (bowheads/arviq) [Georg et al. 2011] live at high latitudes and similar the longest-lived animals, the quahog clam Arcitica islandica lives in Arctic waters [Strahl et al. 2007].

Larger animals live usually longer [Ricklefs, 2008]. Some arctic birds have high levels of oxidative defence. For instance, when foraging conditions deteriorate, some species (e.g. penguins) display no oxidative damage presumably because of greater oxidative defence [Beaulieu et al. 2011]. Both albatrosses and terms exhibit no detectible physiological senescence with advancing age [Lecomte et al. 2010; Nisbet, 2001]. In such, seabirds experience the calamity of so long life [Rowe, 2008:623].

The little brown rats are quite small and remarkable long-lived, with Myotis lucifugus surviving over 34 years and Myotis brandti being capable of surviving at least 41 years. These species exhibit the largest known ratio of longevity/body-size in the whole animal kingdom and are major outliers to the body mass - lifespan correlation [19962715].

Moles

Naked Mole Rat
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Naked mole rats (NMR) are the longest-lived rodents with a maximum lifespan of 32 years, though they are just about the size of mice or rat which only lives about 3 years. Compared to the human body, the body of this tiny rodent shows little decline due to aging, maintaining high activity, bone health, reproductive capacity, and cognitive ability throughout its whole lifetime. These animals also appear not to develop cancer, do not maintain stable body temperature, can live at low oxygen (i.e. high carbon dioxide) concentrations and even do not feel pain. The NMR is a subterranean rodent native to East Africa. They are strictly subterranean and live in colonies with a queen and represent one of only two known eusocial mammals. The naked mole rat shows negligible senescence and no age-related increase in mortality as well as high fecundity until death. Naked-mole rats live in full darkness, at low oxygen, but high carbon dioxide concentrations and are unable to sustain thermogenesis nor feel certain types of pain [Anisimov et al. 2012].

The NMR is the only known mammalian species that does not exhibit the typical age-associated increase in mortality [18180931]. In hundreds of animals, neoplasia has not been observed [16339321] The NMR is resistance to other age-related diseases [21411857; 17468332].

The genome of the NMR, although it is to 85% genetic similar to humans, features its unique adaptations consistent with cancer resistance, poikilothermy, hairlessness, altered visual function, circadian rhythms and taste sensing as well as insensitivity to low oxygen [Anisimov et al. 2012]. Specifically, their genome displays a reduced level of polymorphism and have for instance altered sequence of a key thermoregulator UCP1 and unique sequence of the tumor suppressor p16 [Gladyshev et al. 2011]. What makes this little creatures so resistance against aging? It is a real small wonder; naked-mole rats show no increase in the probability of death. Naked mole rats latently defy the free radical theory of aging. Mole-rat's lipids, proteins and DNA exhibit to eight times more free radical damage than the same molecules in mice. Both mole-rats and long-lived bats have remarkable low insulin levels. Dietary restricted rodents have also low insulin levels and among the men participating in the Baltimore Longitudinal Study of Aging those with lower blood insulin levels have tended to live longer. Naked mole rats might contain special chaperone proteins that help keep various other key proteins in good working order.

Even at young age, lipid peroxidation and iron levels were at least two-fold higher than in mice. Levels of lipid damage do not change with age in mole-rats [Andziak and Buffenstein, 2006; 17129214].

Naked mole rats maintain exceptional protein integrity throughout their long and healthy life as naked-mole-rat liver cells have a greater number of proteasomes and higher protein-disposal activity. They also exhibit a large numbers of immunoproteasomes, which remove antigens after presentation in the immune system and are normally more commonly found in the spleen and thymus [Scientists Find Differences In Long-Lived Rodent's Protein Handlers more]. Thus, the NMR is special in several ways as it is highly cancer resistant and maintains protein integrity in the brain despite exposed to oxidative damage [http://www.biocompare.com/Life-Science-News/116433-Naked-Mole-Rat-May-Hold-The-Secret-To-Long-Life/].

Specifically, NMR have significantly higher chymotrypsin-like (ChT-L) activity and two-fold increase in trypsin-like (T-L). The 20S proteasome is more active and the 26 proteasome was both more active and more populous. Both 19S subunits and immunoproteasome catalytic subunits are present in greater amounts in the NMR, indicating that the higher specific activity may be due to the greater proportion of immunoproteasomes in livers of healthy young adults. Thus, the proteasomes of NMR are primed for the efficient removal [Rodriguez et al. 2012].

From the infancy (1 day) to old age (26 year), naked mole rats have the highest level of growth factor NRG-1 in the cerebellum (the part of the brain important for motor control), which level are sustained throughout their life, from development through adulthood. Levels of NRG-1 are essential for normal brain functioning as it acts as a neuroprotector, safeguarding the integrity of neurons, which may contribute to the resistance of NMR to aging.

Comparing lifelong NRG-1 levels across seven species of rodents, from mice and guinea pigs, to blind mole rats and Damaraland mole rats revealed that the longest lived members exhibit the highest lifelong levels of NRG-1 with the naked-rat mole haven the most robust and enduring supply. In contrast, in both mice and humans, NRG-1 levels go down with age. The correlation between lifespan and NRG-1 levels is independent of evolutionary lineage, meaning that it is unique to the naked mole rat, not a common trait of these rodent species. It appears that it is not the amount of oxidative damage an organism encounters that determines species lifespan but rather than that the protective mechanism may be much more important [http://www.biocompare.com/Life-Science-News/112845-Long-Lived-Rodents-Have-High-Levels-Of-Brain-Protecting-Factor/].

Thus, the naked-mole rat keeps up the integrity of proteins in various organs such as liver, kidney, muscle and brain. Naked mole rat cells are hypersensitive to contact inhibition and arrest proliferation at low cell density. Early contact inhibition is triggered by a extracellular matrix component, requires the activity of p53 and Rb pathways and is associated with induction of p16INK4a, which contributes to this species extraordinary cancer-resistance.

Blind Mole
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The blind mole rat is quite long-lived as it can live up to 21 years and resistant to cancer too. This animals also live under the ground in darkness, scarcity of food, immense numbers of pathogens and low oxygen levels. In such they seem to have evolved a range of mechanisms to cope with a problematic environment. Cell cultures from two species of blind mole rat, Spalax judaei and Spalax golani, behave in ways that render them impervious to tumour growth. These creatures appear to have evolved a different way of this from that observed in the their similarly cancer-resistant cousin, the naked mole rat. While the naked-mole rats cells exhibit extraordinary contact-inhibition ("clausotrophic") and therefore ceasing to divide much sooner than cells from other species, those of the blind mole rats commit mass suicide when overcrowded, preventing uncontrollable proliferation. It seems like that this concert cell death is triggered by the collective release of interferon-beta (IFN-β) [23129611; http://www.nature.com/news/blind-mole-rats-may-hold-key-to-cancer-1.11741].

Whales

Whales can live over 210 years. One of the oldest mammals on the planet may be the Bowhead Whale (a baleen whale) [http://www.epinions.com/content_4076773508?sb=1]. The bowhead whale (Balana mysticetus) has been estimated to live over 200 years [George et al. 1999].

Turtles do not really die of old age. If turtles do not get eaten, crashed by accident or fall prey to a disease they might just live indefinitely. The liver, lungs and kidney's of a centenarian turtle are virtually indistinguishable from a young one [http://www.nytimes.com/2006/12/12/science/12turt.htm?&amp]pagewanted=all].

Green sea turtles take up to a maximum of estimated 50 years to just reach maturity in the wild. Their lifespan is still being documented and believed to be much higher than previously thought [http://www.epinions.com/content_4076773508?sb=1].

Fishes

Some species exhibit both traits (mortality and immortality) such as the Flounder and Rockfish. While the male Flounder reaches a fixed body size and ages normally, the female ones grow indefinitely and exhibit no signs of aging or loss of function with time. To the Rockfish belong both short-lived and long-lived members in the same genus. The lifespan ranges from 12 years for the calico rockfish to 205 years for the rougheye rockfish [http://www.epinions.com/content_4076773508?sb=1].

Growth has physical limits because the needs for muscle, bones and arteries grows faster than the bulk. Radiating heat becomes harder with increased size. Scaling is therefore an issue (it is more an issue on land than in the water). It would be interesting to know if animals have been observed to grow to a size where they are not physically competent any more?

Immortals

Species in which the mortality rate does not increase after maturation are defined as biologically immortal. There are even many cases in plants and animals where the mortality rate actually decreases with age. The life-expectancy of animals with negligible senescence is limited by diseases, predators, or starvation. Several of them have no fixed body size (like some lobsters, flounders, sturgeons, sharks, alligators, turtles, and whales) as they simply increase in body size with time while exhibit no noticeable sign of aging. They rarely become giants because they have succumbed to the perils of living in the wild. However, in capacity (like those that are kept in zoos) they simply grew indefinitely, with almost no decrease in their physiological functions - even after reaching full sexual maturity. In contrast to animals with fixed lifespans, those immortals become more fertile as older they get [http://www.epinions.com/content_4076773508?sb=1].

Sea Urchin

Some species of sea urchin exhibit negligible senescence. Strongylocentrotus purpuratus exhibits age-related changes in gene expression in ubiquitin-proteasome pathway, DNA metabolism, signaling pathways and apoptosis. Components of notch signaling increases in expression in all three tested tissues (muscle, esophagus and nerve), while Wnt1 decreases in both muscle and nerve [Loram and Bodnar, 2012].

Lobster

The lobster (Homarus americanus) age so gracefully that they exhibit no measurable signs of aging: no loss in appetite, no metabolic changes, no loss in reproductive urge or ability nor decline in strength or health. If a lobsters dies it seems to be due to external causes: fished by humans, eaten by seals, wasted by parasites, but they do not appear to die from within. Their organs of the lobster exhibits high telomerase activity [9849895].

Jellyfish

Some jellyfish do not age. For instance the Turritopsis nutricula can revert back to the polyp stage after becoming sexually mature through a process of transdifferentation. It is capable of reversing its life-cycle (i.e. becoming very young again) until it reaches its earliest stage of development and ends up back in embryonic stage. In such it can celebrate its own rebirth. Rejuventation of Turritopsis dohrnii and some other members of the genus is triggered by environmental stress or physical assault. Under poor living conditions it develops back into undifferentiated stem cells of which a polyp arises. If the conditions are improving it simple resets its life program [http://www.nytimes.com/2012/12/02/magazine/can-a-jellyfish-unlock-the-secret-of-immortality.html?pagewanted=all&amp]_r=0].

Sea Squirts

Sea squirts rejuvenate themselves by activating telomerase and they have a special ability to discard junk from their cells. Older parts of the animal are quite simply broken down, and are partially recycled, while new and healthy parts grow out from the adult body.

Hydra

The small sea-water pylop Hydra displays no signs of aging and is potentially immortal.
Hydra exhibits an unlimited lifespan due to the indefinite self-renewal capacity of is stem cells.
Hydra vulgarisis a member of the phylogenetic old phyla Cnidarian, a type of metazoan.
It neither appears to age nor to exhibit decline in reproductive rates, it simply does not undergo senescence [9615920] and therefore achieves biological immortality.

Adult Hydra vulgaris have three stem cell populations (ectodermal and endodermal epitheliomuscular stem cells and interstitial stem cells). The two epitheliomuscular stem cell lineages are multipotent and shape the body, while the interstitial stem cells have a wider developmental potency and gives rise to both somatic cells and gametes [22689361]. Telomeraseprotects the somatic cells of the Hydra. The single FoxO gene in Hydra is expressed at high levels. FoxO is one of the critical drivers of continuous self-renewal capacity [23150562]. It is expressed in all three stem cell types and downregulated upon terminal differentiation in both head and foot tissue as well as differentiating gametes in the gonads. Transgenetic overexpression of FoxO appears to induce expression of stem cells genes in terminally differentiated somatic cells, while FoxO loss-of function via RNAi (silencing) in epithelial cells increases the number terminal differentiated foot cells as well as causes the downregulation of stem cells genes and changes the expression of gene controlling the functionality of the innate immune system [http://www.focus.de/gesundheit/news/geheimnis-ewigen-lebens-gelueftet-forscher-entdecken-das-unsterblichkeits-gen-foxo_aid_861836.html; http://idw-online.de/pages/de/news506619] 20657733].

Ecological Niches

Longevity and immortality can only evolve if the ecological niche does not exhibit any pressures to maintain aging systems. Most of this places provide isolation from other species (predators and competitors).

Desert

There are many long-lived species where the main force of mortality does not evolve (like drought). What also be can found there is sexless species (like the New Mexico whiptail). Diversity is not an advantage to surviving drought. Drought is always the same. Sex and aging come in handy if the main force of mortality also evolves (predators). Thus there is much more diversity towards the equator and rain forest, where the environment generally is agreeable. The main force of mortality here would be evolving predators. In such sex and aging are two sides of the same coin, i.e. the conservators of group diversity as defences to evolving predation. In places like the desert where is mostly drought sexless and long-lived species could evolve because of the lack of predators. For instance the creaosote bush can live 10.000 years and reproduces clonally. Desert plants usually live a long time. Most animals living in the desert are also exceptional long-lived such as the desert tortoise [http://www.ehow.com/about_7230479_baby-desert-tortoise-pet-information.html]. Drought, i.e. the lack of water always kills the same way, it never evolves. Therefore, if this is the main risk, diversity is actually bad for the group and every individual tries to achieve the same perfect defence to dehydration. So any difference from an optimal model is negative and selected against. Thus even sex can be done away along with aging, because there is no need for diversity if isolated in the desert.

Underground

Well protected and preserved environment like the underground allowed the evolution of extra-ordinary long-lived species, such as the longest-lived rodent, the naked-mole rat which live in African underground in mazes made of extensive tunnels that are climatological stable and cut-off from the above-ground world. Thus rendering predation nearly impossible. These barrows contains nest-chambers, tended by sterile workers, and several toilets, which are used to avoid contamination of the living places. These strictly subterranean animals dig through the soil and locate the roots, tubers, and bulbs they eat. In such, this species adapted to a lifestyle in an totally isolated bunker, which enabled the inactivation of several aging-systems over time.

Underwater

Several underwater organisms reproduce asexually and can achieve eternal life. Telomerase is very active in underwater animals like sea squirts, Hydra, and some special kind of Jelly fishes and Corals which are capable of achieving immortality.

Due to the asexual reproduction the child will obtain the same qualities of mother with a very little genetic variation. This renders the child vulnerable to the changing climatic conditions.

Conclusion

A common pattern that emerges is that those species which life extraordinary long have gained this ability though adaption to specific ecological niches or abilities which enabled them to avoid predation and competitors (flight, armour, isolation or intelligence). Without predation both aging and sex which drive diversity become less important. As result defined aging systems become deactivated. The existence of non-aging animals indicates that pro-aging and anti-aging genes exists. Learning from these genetic adaptions will certainly teach us how to make aging also in humans negligible.